It is known in the art how to stabilize silver halide emulsions with respect to shelf stability with an azaindene as illustrated, for example, in U.S. Pat. Nos. 2,444,607; 2,444,609; 2,449,225 and 2,450,397. In these listed patents, the efficacy of various azaindenes is illustrated when they are incorporated as solutions at pH 7-10 into silver halide emulsions. The patents are silent with respect to spectral sensitization of the silver halide grains.
U.S. Pat. No. 2,743,180 is directed to the treatment of unsensitized and optically sensitized silver halide emulsions with polyalkylene oxides and pentazaindenes to stabilize emulsions upon storage.
U.S. Pat. Nos. 2,772,164; 2,835,581 and 3,333,961 are directed to chemically or optically sensitized silver halide emulsions containing, as antifoggants, specified classes of triazaindenes, tetrazaindenes and pentazaindenes.
U.S. Pat. Nos. 3,418,130; 3,462,272 and 3,563,755 are directed to silver halide emulsions containing, as antifoggants, specified classes of tetrazaindenes. It is stated that these compounds do not result in the reduction of sensitivity when used. The only teaching relevant to their use is that they are added after digestion.
U.S. Pat. No. 3,161,506 is directed to color diffusion transfer processes and elements which include an optically sensitized silver halide emulsion having a dye developer associated therewith wherein the emulsion contains a member of the class consisting of hydroxy and amino triazaindenes, hydroxy and amino tetrazaindenes and hydroxy and amino pentazaindenes. The patent merely states that the emulsions contain the specified compounds; it is silent with respect to the manner of incorporating the compounds therein.
Copending application Ser. No. 918,841 filed June 6, 1978, now abandoned (commonly assigned) discloses and claims silver halide emulsions which are stabilized against the build-up of fog centers during storage without adversely affecting spectral sensitization by the following procedure:
(a) spectrally sensitizing silver halide grains with one or more spectral sensitizing dyes;
(b) lowering the pH of the emulsion from a first pH at which the silver halide grains were formed to a second pH of about 5.5 to 4.0, and/or increasing the Br ion/Ag ratio to at least 5 mg Br/gAg; and, subsequent to steps (a) and (b),
(c) adding 5 to 80 mg/gAg of a stabilizer selected from the group consisting of an hydroxy triazaindene, an amino triazaindene, an hydroxy tetrazaindene, an amino tetrazaindene an hydroxy pentazaindene and an amino pentazaindene.
1-phenyl-5-mercaptotetrazole is also known in the art as an emulsion stabilizer.